* Copyright (c) 2015 Google, Inc
* SPDX-License-Identifier: GPL-2.0+
* ARCH_DMA_MINALIGN is defined in asm/cache.h for each architecture. It
* is used to align DMA buffers.
* The ALLOC_CACHE_ALIGN_BUFFER macro is used to allocate a buffer on the
* stack that meets the minimum architecture alignment requirements for DMA.
* Such a buffer is useful for DMA operations where flushing and invalidating
* the cache before and after a read and/or write operation is required for
* correct operations.
* When called the macro creates an array on the stack that is sized such
* 1) The beginning of the array can be advanced enough to be aligned.
* 2) The size of the aligned portion of the array is a multiple of the minimum
* architecture alignment required for DMA.
* 3) The aligned portion contains enough space for the original number of
* elements requested.
* The macro then creates a pointer to the aligned portion of this array and
* assigns to the pointer the address of the first element in the aligned
* portion of the array.
* Calling the macro as:
* ALLOC_CACHE_ALIGN_BUFFER(uint32_t, buffer, 1024);
* Will result in something similar to saying:
* uint32_t buffer;
* The following differences exist:
* 1) The resulting buffer is guaranteed to be aligned to the value of
* 2) The buffer variable created by the macro is a pointer to the specified
* type, and NOT an array of the specified type. This can be very important
* if you want the address of the buffer, which you probably do, to pass it
* to the DMA hardware. The value of &buffer is different in the two cases.
* In the macro case it will be the address of the pointer, not the address
* of the space reserved for the buffer. However, in the second case it
* would be the address of the buffer. So if you are replacing hard coded
* stack buffers with this macro you need to make sure you remove the & from
* the locations where you are taking the address of the buffer.
* Note that the size parameter is the number of array elements to allocate,
* not the number of bytes.
* This macro can not be used outside of function scope, or for the creation
* of a function scoped static buffer. It can not be used to create a cache
* line aligned global buffer.
#define PAD_COUNT(s, pad) (((s) - 1) / (pad) + 1)
#define PAD_SIZE(s, pad) (PAD_COUNT(s, pad) * pad)
#define ALLOC_ALIGN_BUFFER_PAD(type, name, size, align, pad) \
char __##name[ROUND(PAD_SIZE((size) * sizeof(type), pad), align) \
+ (align - 1)]; \
type *name = (type *)ALIGN((uintptr_t)__##name, align)
#define ALLOC_ALIGN_BUFFER(type, name, size, align) \
ALLOC_ALIGN_BUFFER_PAD(type, name, size, align, 1)
#define ALLOC_CACHE_ALIGN_BUFFER_PAD(type, name, size, pad) \
ALLOC_ALIGN_BUFFER_PAD(type, name, size, ARCH_DMA_MINALIGN, pad)
#define ALLOC_CACHE_ALIGN_BUFFER(type, name, size) \
ALLOC_ALIGN_BUFFER(type, name, size, ARCH_DMA_MINALIGN)
* DEFINE_CACHE_ALIGN_BUFFER() is similar to ALLOC_CACHE_ALIGN_BUFFER, but it's
* purpose is to allow allocating aligned buffers outside of function scope.
* Usage of this macro shall be avoided or used with extreme care!
#define DEFINE_ALIGN_BUFFER(type, name, size, align) \
static char __##name[ALIGN(size * sizeof(type), align)] \
static type *name = (type *)__##name
#define DEFINE_CACHE_ALIGN_BUFFER(type, name, size) \
DEFINE_ALIGN_BUFFER(type, name, size, ARCH_DMA_MINALIGN)
* malloc_cache_aligned() - allocate a memory region aligned to cache line size
* This allocates memory at a cache-line boundary. The amount allocated may
* be larger than requested as it is rounded up to the nearest multiple of the
* cache-line size. This ensured that subsequent cache operations on this
* memory (flush, invalidate) will not affect subsequently allocated regions.
* @size: Minimum number of bytes to allocate
* @return pointer to new memory region, or NULL if there is no more memory
static inline void *malloc_cache_aligned(size_t size)
return memalign(ARCH_DMA_MINALIGN, ALIGN(size, ARCH_DMA_MINALIGN));
#endif /* __ALIGNMEM_H */